Inductance coil



Sept. 11, 1951 c. w. N UTTMAN INDUCTANCE COIL 2 Sheets-Sheet 1 FiledAug. 9, 1950 FIG.

X SERIES HW lNl EN TOR C. m NU 7'7'MAN ATTORNEY INDUCTANCE COIL 2Sheets-Sheet 2 Filed Aug. 9, 1950 0 0 w m 0 0 6 u I 0 7 0 5 M G L o n A07 M W J, R N M H 6 w m m F M E R W T n w 8 2 10 M a m R m I 0 a P 0 0 00 0 0 w m m INVENTOR C. W NUT TMAN B) 5 ATTORNEY "ferromagneticmaterial, I ceramic ferromagnetic material known as fer- Patentec] Sept.11, 1951 INDUCTAN CE oQIL p Charles W. Nuttman, East OrangerNrJ assignorto Bell Telephone Laboratories, Incorporated,. New York, N. Y., acorporation of New York Application August 9, 1950, Serial'No.178,40I-QI 'This invention relates to inductance coils and,

more particularly, to such coils having coupled windings.

In certain types of filters and, particularly,

those employing crystal units as elements of the filter, it is desirableto provide coupling between two of the inductances in the filtersectionin order to attain an additional point of infinite at- .tenuationat a finite frequency. By providing slight changes in the percentage ofthe coupling between the two inductances in a filter section, thefrequency at which the additional infinite attenuation occurs is alsochanged, and, therefore, a different filter performance characteristicis obtained.

In such circuits and in other circuits where ,-difierent degrees ofcoupling are required between .windings of the same generalcharacteristics and ,3 form but electrically positioned in difierentparts .of the circuit, it is desirable that a single basic. ,structurebe employed and only slight changes be required during the fabricationof this structure to alter the coupling tothe desired percentage In thisway, uniformity of the various piece parts required for the difl'erentcoupled coils may be obtained with a resultant decrease in the expenseof fabricating the different coils.

It is, therefore, one object of this invention to vary the reluctancesof the possible flux paths in coils of the general type aforementionedduring the fabrication thereof so that asingle basic structure may beemployed for coils of any desired inductive coupling. A I

It is another object of this invention to provide a single basic coilstructure in which the inductive coupling between the two windings can,be facilely predetermined at any value between approximately zeroand 100per cent. 7

It is a further object of thisinvention to improve the facility withwhich such coils are fabricated and to diminish theexpenses ofproduction that have been necessitated by employing different coilstructures and difi'erently dimensioned coil parts for coils withdifferent values of inductive coupling between the windings thereof;

A further object of this invention is to provide an'improved inductancecoil.

1 These and other objects are accomplished in one specific illustrativeembodiment of this invention in which a hollow enclosed casing or a suchas a sintered rite, is divided into two sections or cavities by acentral ring which forms part of the casing and extends into the casing;A center core, which 7 Claims. (01.171442) also may be of ferrite, isplaced in each of these cavities along the axis of the casing, and awinding surrounds each center core. A third center core ispositionedinside the casing medially adjacent the central ring along the same axisas .the other cores andextends slightly into each of the windings.Air-gaps are provided between matelyvzero to per cent.

.each'of' the. three-centercores and between'the twosend center coresand the end sections of the casing by insulating members separating themand between the middle center core and the cen- .tralring. By varyingthese air-gaps in relation to each other, the inductive coupling betweenthe two windings may be varied from approxi- Specifically,ithere may bealtered the reluctances of the paths of" the flux linking each-coilsingly and coupling the two coils by varying the air-gap between thecentral ring and themiddlc center core to particularly affect theindividual flux paths, and by varying theair-gaps in the three piececenter core, and especially the distance the ;midd1e center core extendsinto the windings, to particularly aiiect the inductiv coupling betweenthe two windings.

- It is,- therefore, one feature-of this invention that the enclosedcasing of thecoil be divided into distinct sections or cavities, each ofsaid cavities having a winding therein, and that said cavitiesbemagnetically linked'by a center core member extending between saidcavities and partially into each of said windings.

It is a further feature of "this invention that the casing comprise acentral ring or plate adjacent the above-mentioned center core andextending into the casing towards that center core to divide the easinginto two cavities and to provide a flux path from the casing to thecenter core. .1 ij

It isja stillrfurther feature of this invention that the centralmagnetic path in the casing comprise a plurality of center cores axiallyaligned and separated from each other and from the end sections ofthecasing, the distances between the cores themselves and the endsections providing "from consideration of the following detailed de i nl; thea sgimpan i i n wh h unit |3 between the two windings.

Fig. 4 is a graph illustrating the percentagechange in the inductivecoupling in the coil of Fig. 2 with change in the reluctances of theflux paths shown in Fig. 3 by variation of the lengths of the radial andcentral air-gaps.

Referring now to the drawing, Fig. 1 is a schematic representation of acrystal channelfilter using coils having controlled coupling between thewindings of each coil. The first coil comprises a first winding H and asecond winding |2 placed in series opposing. and with a crystalSimilarly, the second coil comprises a first winding l4 and a secondwinding |5 in series opposing and with a crystal unit l6 between the twowindings. The percentage of coupling between the windings of the twocoils may be different; thus, in one illustrative channel filtercircuit, the percentage coupling between the windings II and I2 may be17.09 per cent, and the percentage coupling between the windings l4 andI5 may be 19.10 per cent. However, in accordance with this invention,both' coils may advantageously be constructed in the same generalstructure and from the same component parts as in the illustrativeembodiment of this invention shown in Fig. 2.

As seen in that figure, the coil windings and 2| are completely enclosedwithin a cylindrical casing, the casing being made up of two cupshapedmembers 22 and 23 and an annular center plate 24 between them, thecasing and other members forming portions of the flux paths of the coilbeing advantageously of a ferromagnetic material and, particularly, of asintered ceramic ferromagnetic material known as ferrite. Thus, themagnetic portions of the coil may advantageously be of a manganese-zincferrite. In the specific embodiment illustrated in the drawing, thecup-shaped members were themselves constructed of several componentparts including end plates 25 and rings 26; however, the cupshapedmembers may be made in one piece if desired. Each end plate 25 has anaperture 21 axially therein, the purpose for which will be discussedbelow, and apertures 28 through which the leads 29 of the coils 20 and2| extend. Insulating grommets 30' are positioned in the apertures 28around the leads 29.

The annular center plate 24 extends inwards into the casing further thanthe sides of the cupshaped members 22 and 23, or, in this specificembodiment, further than the rings 26. The annular center plate 24 thusdivides the easing into two equal cavities 33 and 34. Winding 20 isplaced axially in cavity 33 and winding 2| axially in cavity 34. Threecenter cores 36, 31, and 38, defining a center post, extend axiallybetween the two end plates 25, being separated 'from them and from eachother by air-gap spacers 39, which may be of paper or other insulatingmaterial. The spacers 39 are advantageously approximately equal as themaximum Q is attainable when the central air-gaps defined by thesespacers are approximately equal. The spacers 33 and the cores 36, 31,and 3B are axially apertured and provide, with the apertures 21 in theend plates 25, an open path through the casing, the reason for whichwill be discussed below.

The winding 20 is supported on the center core 36 in the cavity 33, andthe winding 2| is supported on the center core 38 in the cavity 34. Themiddle center core 31 is adjacent the center ring or plate 24 andextends partially into a each cavity 33 and 34 and into each winding 20and 2|. The windings may be secured directly to the cores, as shown, or,if it is intended to operate coils constructed in accordance with thisinvention at higher voltages than those generally encountered in channelfilters, the windings may be wound on insulating spools and the spoolsse cured to the center cores in ways known in the art.

The casing is clamped between two clamping plates 4|, which may besquare, by clamping screws 42 and nuts 43. The clamping plates 4| haveapertures centrally therein aligned with apertures 21 in the end plates25 and apertures 45 aligned with apertures 23 in the end plates 25 andthrough which apertures 45 the lead .wires 29 extend. The insulatinggrommets or tubing 35 may also extend into or through the apertures 45.

Referring now especially to Fig. 3. there are three magnetic circuits orpaths provided by the above-described arrangement of cup-shaped members,center ring and cores. Magnetic flux may follow the patl 1 5|) definedby the center core 36, part ofthe center core 31; the ring-24, and thecup-shaped member 22 and thus not link the coil 26 with the other coilat all. Similarly, there is a flux path 5| around the cavity 34 forwhich there is no couplingbetween' the coils. However, there is also apossible flux path- 52 through the three cores 36, 31, and 38, throughthe rim of the ring 24, and the cup-shaped members 22 and 23, all ofwhich flux would link both windings 20 and 2|.

It is thus apparent that the flux from each winding that follows thepaths 5!! or 5| links only the turns of its own winding, whereas theflux from either winding that follows the path 52 links the turns ofboth windings, inductively couplingthem. It has been found that thisinductive coupling between the two windings may be varied betweenapproximately zero and 100 per cent by varying the reluctances of thesethree fiux paths and, specifically, by varying the ratio of the lengthsof the air-gaps in the individual winding flux paths 5B and 5| and thelengths oftheair-gaps in the coupling flux path 52. Thus, the percentageof the inductive coupling between the two windings may be decreased byincreasing the air-gaps in the central post of the coil, i. e., betweenthe center cores 36, 31, and 38 and between these coils and the ends ofthe cup-shaped casing members 22 and 23; or the percentage of theinductive coupling may be decreased. by decreasing the radial air-gapbetween the central annular plate 24 and the middle center core 31. Thefirst alteration of the air-gaps primarily affects the flux path 52 byincreasing the reluctance of that path,as that path includes each of thefour air-gaps formed between the center cores and the casing ends. Thesecond alteration of the air-gaps primarily affects the flux paths and5| by reducing the reluctance of those paths. The per.- centage ofcoupling can similarly be increased by the opposite of these air-gapvariations.

-LIt .has-been found that. in the fabrication 101 these .coils, whenboth variations. of air-gap spacings from the base value or norm areincorporated in the coil so that their efiects are cumulative, theinductive coupling can be varied 6 Fig. 4 graphically represents thisdata, curve 56 being drawn for the constant radial air-gap of .007" andcurve 55 being drawn for the constantradial-air-gap of .014", each beinga curve in this single structural design from approxi- 5 of totalcentral core air-gap as against the per- .mately zero to 100 per centand that. any coucentage of inductive coupling. As is readily applingdesired within these limits may be obtained. parent, the couplingincreases 1 for each curve .The-coil maybe assemblied by a jig having awith-"decrease in the total central air-gap, for n n ma t w l 01 pin tdin upwards the reasons explained above. Similarly, curve and ontowhichthe various parts are placed, the i0 .51 is a curve of radialair-gap against percentage d0we1 e in hr h he apert res 44 oftheinductive coupling for a constant total center 'elamping Platesapertures 27 of the end me .core air-gap of .028"; as is also readilyapparent s e apertured spacers '39, and therhollow .by. this curve, thepercentage of inductive coucenter coremembers-Zili, 31, and 3B.- The rinpling between the coils increases with an in- 26 and annular center plae a p is crease in the radial air-gap, for the reasons ex.- in place onthe jig, as by two semi-cylindrical plajned above I l -D tubes positi din the j and bearing ,,-It, is to be understood that although these snst t e coil etw n clamping plates 4| curves have beenplotted in aspecific percentage to centrally 'lo ate. thes.e members prior. t0. therange of inductive coupling, the coupling may be fin l cla p f thescrews 42 and nuts predetermined at any value from approximately T e igs and core. members 36, 31, and 38 zero to 100 per cent by extensionsof these -may a be initially Of a standardler base size, curves and ofthe principles of this invention, which s may he the largest that isexpected whereby. difierent curves for different valuesof e n e toobtain any of t e percentages of i air-gap lengths are attainable. Thus,by preduetive coupling desired; I In Order to increase 25 paring aseries of curves of, for example, central th length of t e air-gaps inthe Center core airegaplength against inductive coupling fordifassembimjeach ofv the center cores ,36, 31, and..38 f re t constantradial airflgap lengths the .LWouidthen be. slightly .le d in height. asb gap lengths necessary for any desired coupling gr ndin a the p c cas-by can. be read directly off the chart thus prepared ad ih yfi 0f P-between the cores- As and the parts ground or otherwise slightlyvarpOinted Out above, tends t0 decrease the into the lengths thusdetermined In ductive coupling between the two windings 20 way, thecomplete range of inductive coupling 1- ,Similariy 9 decrease the s in,may becovered by a single structure employing th cen er core a t vincrease the Couphhgin each instancethe same piece parts but readily h eof the tgprings 24 may be sli yaried during the fabrication inaccordance with creased, as y. .s nd n ,-as e total length informationeasily obtainable from priorly prelof theospacers 9' h thehehtel coremembers pared charts, thereby allowing a multitude of 3 and 3 equals theh i of the four Outer different coils, as for different locations infilter rings and the center nhg ,circuits, to be fabricated without theequal mul- The radial between the medlahy 40 titude of diiferent partsthat must be stored and cated center core member 31 and the annulardifferently fabri ated Plate ring is determine? by diameter cult is tobeunderstood that the above-described of the core member and the Innerdlametelf of arrangements are illustrative of the application the n As tcore member 37 h lhto of'the principles of the invention. Numerous ,eachof the i and t0 proYlde the other, arrangements may be devised by thosew r t n fl P between them its Outer skilled-in .the art withoutdeparting from the diameter cannot be altered. Thus,,I have found piritand cope of the invention it advisable to vary the radial air-gap andthus @What ishclaimed v ev ry the e u tances of thefiux paths 5 0 and5|. 1. In an inductance coil, a hollow enclosed which link 0 y t pectiwind n by casingsaid casing including a member extendchanging the innerdiameter of the annular plate jng t Said casing and dividing Said hoiiowmember easing into two sections, a center core in each of In certain lat embodiments of this saidsections, a winding around each of saidvention constructed in accordance with Fig. 2 a. middl center coreextending withi and described above, different radial and total saidmember and defining a first air-gap therecentral air-gaps have beenemployed, and-the .with, said, middle core being in juxtapositionfollowing table is exemplary of the variations in with the firstmentioned center cores in said seethe inductive coupling that I havebeen able to tions, said casing and said cores being of a ferobtain withthis single basic structure bymeans romagnetic material, and meansproviding second 01' these different air-gaps: 6O ,airr aps between saidcenter cores whereby the Inductance and Approximate Turns of WindingInductive Coupling Total Air-gap Radial up between Windin Central ingsin the Series Core Assembly gap 20 21 Opposition Connection Per Cent.015" .007" 160 turns, 15.30 mh 47. 0 .028 .007" 160 turns, 7.52 mh 121.3 .028 .014" 212 turns, 11.39 mh. 28.2 .040" .014" 212 turns, 12.30rnh. 18.7

These measurements were made at kilocycles and with .001 ampere throughthe windings 20 and 2|.

percentage coupling between said two windings is determined by therelationship between the lengths of said first and second air-gaps.

casing-whereby. the percentage coupling between said twowindingsisdetermined by the relationship between the lengths of said first andsecond air-gaps.

, 3.-In an inductance coil, a hollow enclosed casing, said casingincluding a member extending into-said casing and dividing said holloweasing into twosections, acenter core in each of said sections, awinding aroundeach of said center cores, a middlecenter core extendingthrough said member and defining afirst air-gap therewith, said casingand cores being of a sintered ceramic ferromagnetic material, saidmiddle core extending-into each of said windings and providing a lowreluctance flux path between said two windings, and means'providingsecond airgaps between said center cores and between the outer ofsaidcenter cores and said casing whereby the percentage coupling betweensaid two windings is determined by the relationship between the lengthsof said first and second gaps.

4. In an inductance coil, a hollow cylindrical body closed atboth ends,said bodyincluding a center ringextending into said hollow body anddividing said hollow body into two sections, a central post ins'aid'bodyg-said central postcomprising a center core in each of said sectionsand a middle center core extending adjacent said center ring anddefining a first air-gap'therewith, said body and said cores being of aferromagnetic material, a winding around, each of said outer cores insaid sections, "and means providing second air-gaps in said central postand between said post and said body, the percentage of-inducti'vecoupling between said windings being determined by the relative widthsof said first and the total of said second air-gaps.

5. In an inductance coil, a hollow cylindrical body'closed at both ends,said body including a center ring extending into said hollow body anddividing said hollowbody into two sections, said body being of aferromagnetic material, a central post in said body, said central postcomprising a center corein each of said sections and a middle centercore extending adjacent said center ring and defining a first air-gaptherewith, said cores being of a ferromagnetic material, a windingaround each of said outer cores in said sections, said middle centercore extending into each of said windings and providing a low reluctanceflux path between said windings, and

means providing second air-gaps .in said central post and between saidpost and said body, the percentage of inductive coupling between saidwindings being determined by the relative widths of said first and thetotal of said second air-gaps. 6. In an inductance coil, a. hollowcylindrical body closed at both ends and having apertures centrallylocated in said ends, said body including a center ring extending intosaidbody and dividing it internally into two sections, a center core--in each of said sections, a middle centerncore' extending between saidsections-adjaoent said ring and defining a radial air-gap therewith,saidbody and said cores being of a ferromagnetic material, said coresbeing aligned axiallyin said body and having apertures there-- throughaligned with said apertures i-n said-ends of said body, a winding aroundeach of said outer cores in saidsections, said middle core extend- -ingpartially 'into each of said windings, apertured spacers between each ofsaid cores and between said cores and said ends of said body, theapertures of said spacers being axially aligned with said otherapertures, said spacers defining a plurality of central air-gaps, thepercentage inductive coupling between said windings being determined bythe relationship between said radial air-gap and the total of saidplurality of central air-gaps, and means clamping said body together.

7 An inductance coil comprising a hollow cylindrical body comprising apair or end members, each of said members having-an aperture centrallytherein, aplurality of ring members,

and a central annular plate member, said annular plate member extendinginto saidbody and dividing said body into two sections, a center coreaxially in each section, a winding'around each center core, a middlecenter core extending axially between said sections adjacent saidannular plate member and defining therewith a radial air-gap, said bodyand said cores being of a sintered ceramic ferromagnetic material, saidmiddle core extending partially into each of said windings, each of saidcores being axially apertured, aperture-d spacers between each of saidcenter cores and between the outer center cores and said end members,the apertures of said spacers being axially aligned with said otherapertures, said spacer members defining four approximately equal centralair-gaps, the lengths of said central air-gaps being determined by therelative lengths of said cores and said rings-the percentage inductivecoupling between said windings being determined by the relationshipbetween said radial air-gap and the total of said four central air-gaps,and means clamping said body together. 1

CHARLES W. NUTTMAN.

No references cited.

